1. Field of the Invention
In these times of uncertainty about the availability of energy supplies, there is substantial interest in discovering ways to increase the usuable amount of liquid hydrocarbon fuels available. One way that this can be accomplished is by adding a non-petroleum derived fuel source to, for example, middle distillate oils.
Various problems have arisen from the extension of middle distillate petroleum fuels with non-petroleum derived fuels, such as those derived from shale oil, tar sands, alcohols, vegetable oils, and other oxygenated materials, or mixtures thereof. It has been found that middle distillate fuels extended with these materials are unable to achieve a sufficiently high rating in the Potential Deposits Test (P.D.), a test method for predicting the storage stability of middle distillates, to allow the fuel mixture to be commercially usable. Fuel mixtures which do not achieve at least a 2 rating in the P.D. test have an unacceptably low stability and are unable to be stored for long periods of time. That is, insoluble material formed during the storage of the fuel material precipitates out from the fuel mixture. If this should occur in an oil storage tank, the precipitated-out material tends to clog the filters which the oil comes in contact with and thus hinders or prevents the oil from being pumped from the facility. Likewise, if this were to occur in the fuel tank of a motor vehicle, the precipitated out material would not only clog the fuel line, but would also cause engine deposits to form, fouling the fuel injectors and interfering with the combustion of the fuel.
2. Description of the Prior Art
Commonly assigned U.S. Pat. No. 2,956,870 discloses a dibenzoate of a polyethylene glycol and a short chain alkoxyalkyl phthalate, having the following general formula: ##STR1## wherein n ranges from 2 to 12, preferably 4 to 8, and n' ranges from 1 to 5, preferably 1 to 2, and R is an alkyl group having from 1 to 6 carbon atoms. This additive when added to an engine lubricating oil composition acts to control deposits in the combustion zone.